The invention relates to an electrically conductive polymeric complex which can be coated on the surfaces of plastics, metals and fibers, or embodied in other polymeric or inorganic materials.
Electrically conductive coatings are used for no-shock rugs, no-cling fabrics, antielectrostatic coatings for packaging materials, low emissitivity garments for better insulation value or infrared camouflage and as antielectrostatic coatings for plastics, glass and other surfaces. The prior art coatings for these purposes are typically ionic conductors or electronic conductors.
Ionic conductors include quaternary ammonium salts and polyelectrolytes. The drawbacks to the effective uses of these conductors are low conductivity and surface resistivities 109 to 1013 ohm per square. The resistivity is humidity sensitive, such that the ionic conductivity is greatly decreased in dry environments.
Electronic conductors, e.g. carbon fibers and antimony-doped tin oxide mixed in polymeric fibers, perform better than ionic conductors because they can achieve higher conductivity and are not as sensitive to humidity levels. However, electronic conductors result in a material which is stiff, fragile and difficult to process. Further, the electronic conductors are difficult to dye.
Intrinsically conducting polymers are not only useful for antielectrostatic applications, they are potentially useful in other fields. They are potentially useful as anticorrosion coatings because of their electroactive interaction with the metal surface. A coating may be applied to windows of a car or a building to reduce heating by sun light because the polymer is effective to prevent the transmission of the near infrared region of the solar radiation while allowing the visible light to pass through. A coating or a fabric-like material that contains the conducting polymer may modify the emissivity of a warm body (human or a vehicle) to camouflage against the detection of night-vision sensors. A material containing a conducting polymer for these applications needs both to be easily applied as a coating material and to be durable as a coating.
Conducting polymers such as single strand polyaniline, have not enjoyed commercial success. They are brittle, very difficult to process and not stable in the conductive state.
A molecular complex of polyaniline and a polyelectrolyte which is processable, is disclosed in U.S. Pat. No. 5,489,400. As disclosed in this patent, the mole ratio of aniline monomer to the acid functional group (polyelectrolyte) was less than one. When the mole ratio was increased beyond one, the molecular complex become insoluble in solvents and was difficult to use in coating or dying processes. Further, the electrical conductivity of the molecular complex disclosed in that patent diminished when the molecular complex was used in a dye or coating.
The present invention is directed to a polymeric complex of a conducting polymer and a polyelectrolyte where the mole ratio of the conducting polymer to the acid functional groups of the polyelectrolyte is greater or equal to one. The polymeric complex described herein is easily processable for coating and mixing applications.
The invention, in another embodiment, is directed to the method of synthesizing the polymeric complex.
The invention in still another embodiment relates to the coatings and compositions based on the polymeric complex.
The present invention discloses a new processable electrically conducting polymer complex and a synthesis for making the same. These processable complexes comprise certain polyelectrolytes and a conducting polymer. The polymeric complex is made by template guided chemical polymerization and contains a polyelectrolyte and a conducting polymer. The polyelectrolyte carries a net negative electrical charge and the conducting polymer carries a net positive electrical charge. Alternatively, the polyelectrolyte can carry a net negative electrical charge and the conducting polymer is in its non-conductive electrically neutral state. Optionally, the polyelectrolyte carries a net positive electrical charge and said conducing polymer in its nonconductive electrically neutral state. In addition, the polymeric complex of this invention can comprise at least two types of polyelectrolyte and one type of conducting polymer.
The polymeric complex is an electrically conducting complex which is suspendable in water. The complex is easily processed such that it can readily be applied by a coating, brushing, spraying, roller, etc. The polymeric complex is washable whether admixed with other polymers or coated on fabrics or hard surfaces. Alternatively, the molecular complex can be admixed with other materials such as epoxy, poly(vinyl butyreal) and NYLON(copyright) as polymer blends.
This invention, in one embodiment, relates to a synthesis that leads to the conducting polymeric complex that is a suspension or dispersion in water or aqueous solution. It is processable as a water-borne coating material. The water-borne conducting polymer is, however, insoluble in water once it is dried as a coating on a substrate. This property makes it advantageous. Although the prior art teaches polymeric complexes can be made soluble in water, so a coating can be also made by evaporation of the water, the coating is not durable because it is easily redissolved by water. The truly water soluble conducting polymers can not be used as antielectrostatic coatings if the surface is to be in contact with water or moisture. The prior art water soluble polyaniline is also not useful as anticorrosion coating materials because of the extensive swelling or dissolution in ambient environment.
In a preferred embodiment, the invention is a double strand conducting polymeric complex. One strand is a conducting polymer, preferably polyaniline, which has high electrical (not ionic) conductivity. The other stand is a polyelectrolyte which provides the sites for functionalities. The polyelectrolyte also provides stability to the conducting polymer, processability to the conducting polymer and maintains the conductivity of the conducting polymer in saline water, moisture and solvents, environments of high temperatures, e.g. 200xc2x0 C. The mole ratio of the aniline to the functional group is greater than 1:1 and the polymeric complex can be suspended in a water or water/alcohol mixture. The ratio of the aniline to acid functional group can be increased to more than 4:1 while still maintaining the properties of processability.
The polyelectrolyte is selected to provide adhesion to textile fibers either by absorption into the fibers, by chemical binding, or by polymer chain tangling or interlocking with the fibers. The conducting polymer resists water induced protonation and is washable in neutral water. Typically prior art conducting polymers deprotonate in water.
The polymeric complex of the invention is an aqueous based composition and can be applied by painting, spraying, dipping, screen printing or any of the known coating techniques, i.e. roll to roll, doctor blade, etc. The complex is suspended as microaggregates in water and is blendable with other polymers or dyes.
The polymeric complexes disclosed herein have higher electrical conductivity than the molecular complexes of the prior art and are still processable (blendable and dispersible).